Re: Problems loading firmware using built-in drivers with kernels that use initramfs.

From: Takashi Iwai <tiwai@suse.de>
To: Ming Lei <ming.lei@canonical.com>
Cc: "Luis R. Rodriguez" <mcgrof@suse.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Liam Girdwood <liam.r.girdwood@linux.intel.com>,
	"Jie, Yang" <yang.jie@intel.com>,
	Dmitry Torokhov <dmitry.torokhov@gmail.com>,
	"joonas.lahtinen@linux.intel.com"
	<joonas.lahtinen@linux.intel.com>, Tom Gundersen <teg@jklm.no>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Kay Sievers <kay@vrfy.org>, David Woodhouse <dwmw2@infradead.org>,
	Luis Rodriguez <mcgrof@do-not-panic.com>,
	lkml <linux-kernel@vger.kernel.org>,
	yalin wang <yalin.wang2010@gmail.com>
Subject: Re: Problems loading firmware using built-in drivers with kernels that use initramfs.
Date: Sat, 29 Aug 2015 09:11:27 +0200	[thread overview]
Message-ID: <s5hzj1algbk.wl-tiwai@suse.de> (raw)
In-Reply-To: <CACVXFVMp88FtcC0vGr802aG9p7bG3S2Gm0ZAKKkcikCK6ygPeQ@mail.gmail.com>

On Sat, 29 Aug 2015 06:09:01 +0200,
Ming Lei wrote:
> 
> On Sat, Aug 29, 2015 at 9:11 AM, Luis R. Rodriguez <mcgrof@suse.com> wrote:
> > On Thu, Aug 27, 2015 at 08:55:13AM +0800, Ming Lei wrote:
> >> On Thu, Aug 27, 2015 at 2:07 AM, Linus Torvalds
> >> <torvalds@linux-foundation.org> wrote:
> >> > On Wed, Aug 26, 2015 at 1:06 AM, Liam Girdwood
> >> > <liam.r.girdwood@linux.intel.com> wrote:
> >> >>
> >> >> I think the options are to either :-
> >> >>
> >> >> 1) Don not support audio DSP drivers using topology data as built-in
> >> >> drivers. Audio is not really a critical system required for booting
> >> >> anyway.
> >> >
> >> > Yes, forcing it to be a module and not letting people compile it in by
> >> > mistake (and then not have it work) is an option.
> >> >
> >> > That said, there are situations where people don't want to use
> >> > modules. I used to eschew them for security reasons, for example - now
> >> > I instead just do a one-time temporary key. But others may have other
> >> > reasons to try to avoid modules.
> >> >
> >> >> 2) Create a default PCM for every driver that has topology data on the
> >> >> assumption that every sound card will at least 1 PCM. This PCM can then
> >> >> be re-configured when the FW is loaded.
> >> >
> >> > That would seem to be the better option if it is reasonably implementable.
> >> >
> >> > Of course, some kind of timer-based retry (limited *somehow*) of the
> >> > fw loading could work too, but smells really really hacky.
> >>
> >> Yeah, years ago, we discussed to use -EPROBE_DEFER for the situation,
> >> which should be one kind of fix, but looks there were objections at that time.
> >
> > That would still be a hack. I'll note there is also asynchronous probe support
> > now but to use that would also be a hack for this issue. We don't want to
> 
> If we think firmware as one kind of resources like regulators, gpio and others,
> PROBE_DEFER is one good match for firmware loading case, and
> it has been used by lots of drivers, so why can't it be used for
> firmware loading?
> 
> One problem is that we need to convert drivers into returning -EPROBE_DEFER
> in case of request failure, and that may involve some work, but which
> should be mechanical.

I find such a delaying mechanism not so bad, too.  It's very
straightforward, at least, no big pain in the transition in the driver
side.

> > encourage folks to go down that road.  They'd be hacks for this issue as you
> > are simply delaying the driver probe for a later time and there is no guarantee
> > that any pivot_root() might have already been completed later to ensure your
> > driver's fw file is present. So it may work or it may not.
> 
> We can trigger defer probe explicitly once root fs is setup or other condition
> is met.

Right, how to trigger the reprobe (and relevant optimization) needs to
be considered on top of the current mechanism.

Takashi